Ya some it may i suppose..... (Like XP SP3 causes issues ONLY IN SOME MACHINES)

Well i imagine that a slow computer can be attributed to a bottleneck in the default software clock speeds. But I don't think this is the norm, and usually most computers are bottlenecked by their CPU and hardware bus speeds (not to mention the worst bottleneck of all, your harddrive). If it even does change the software clock speeds, this would likely cause syncronization issues with software written that relies on these clock speeds to be something reasonable.